System for generating high fuel pressure for a fuel injection system used in internal combustion engines

ABSTRACT

The invention relates to a system for generating high fuel pressure for a fuel injection system used in internal combustion engines in which via a low-pressure pump fuel aspirated from a fuel tank is delivered via a low pressure line and at least one valve to a high-pressure pump, and some of the fuel stream is diverted to the return loop from the low pressure line at or upstream of the high-pressure pump. In the low pressure line, an electrically controlled flow regulating valve is inserted between the low-pressure pump and the high-pressure pump. The flow regulating valve splits the fuel stream supplied. One portion is delivered to the high-pressure pump, and the remainder is relieved into the return loop. The flow regulating valve requires little space and only a few connections and is simple to manipulate.

PRIOR ART

The invention is based on a system for generating high fuel pressure fora fuel injection system used in internal combustion engines.

One such system is known from European Patent Disclosure EP 0 270 720A1. There, on the one hand a high-pressure pump downstream of alow-pressure pump is described, and on the other a controller comprisinga plurality of hydraulic valves is described. The valves are used tosplit the volumetric flow furnished by the low-pressure pump into a workflow to be delivered to the high-pressure pump and a residual flow to berelieved into a fuel tank. The valves include at least one pressurelimiting valve integrated into a return line and optionallyremote-controlled. Also built into the low pressure line alternativelyare a throttle valve, a throttle valve adjustable under remote control,a 2/2-way valve and a 3/3-way valve. These last two valves are alsoremote-controlled.

In the prior art, to control a feed quantity of the low-pressure pumpthat is virtually dependent on fuel demand, hydraulic component groupsare needed that always include a plurality of components.

ADVANTAGES OF THE INVENTION

In the subject of the invention, an electrically controlled flowregulating valve is used in the low pressure line between thelow-pressure pump and the high-pressure pump. The valve splits thesupplied fuel stream. One part is delivered to the high-pressure pump,and the remainder is relieved into the return loop. The remaining fuelcan be used in Diesel engines and others for lubricating thehigh-pressure pump.

The flow regulating valve, which for instance is an electromagneticallyactuated longitudinal slide valve, is incorporated directly into the lowpressure line. It requires little space, only two connections that areunder fuel pressure, and an electric trigger line. In this way, it iseasy to install and to replace.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Further details of the invention will become apparent from the ensuingdescription of a schematically shown embodiment:

FIG. 1: a hydraulic circuit diagram for a system for generating highfuel pressure with a symbolically shown low-pressure pump and asymbolically shown high-pressure pump, and

FIG. 2: the flow regulating valve in longitudinal section.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 shows some essential portions of a system for generating highfuel pressure in internal combustion engines. The fuel, which is underhigh pressure, is delivered to a downstream fuel injection system.

For generating high fuel pressure, the fuel is aspirated from a fueltank (1) by means of a low-pressure pump (3), which for instance iselectrically driven, and is pumped via a flow regulating valve (40) to ahigh-pressure pump (20) and/or into a return line (13). A filter (2) isbuilt into a suction line (11) disposed between the fuel tank (1) andthe low-pressure pump (3). A fine filter (4) is integrated into a lowpressure line (12) located between the flow regulating valve (40) andthe high-pressure pump (20).

The low pressure line (12) leads to the inlet check valve (31) of thehigh-pressure pump (20). By way of the previous mentioned valves, whichare disposed on or in the high-pressure pump (20), the fuel reaches thecylinder chambers (24). In the three-cylinder high-pressure pump (20)shown, one high-pressure piston (29) moves in each cylinder chamber(24). The piston is guided in a cylinder (23). The high-pressure piston(29) is moved in at least a compression stroke via an eccentric (22) orcam, supported in an eccentric housing (21), with the interposition ofan intermediate piston (26). In this process, the intermediate piston(26) pushes the high-pressure piston (29) in front of it. The quantityof fuel present in the cylinder chamber (24) is thus forced into a highpressure line (14) via an outlet check valve (32). Via the high-pressureline (14), the fuel is pumped into a high-pressure fuel reservoir, notshown.

In the intake phase, or as the eccentric stroke is decreasing, theintermediate piston (26) is moved by means of a compression spring (28)toward the center line of the eccentric housing. The high-pressurepiston (29) is forced backward by the fuel flowing in via the inletcheck valve (31). The return stroke is dependent on the quantity of fuelfurnished via the inlet check valve (31). If the engine at low partialload or in idling, for instance, for instance requires only little fuelthen the return stroke of the high-pressure piston (29) is short. Theintermediate piston (26) in the next working stroke comes into contactwith the high-pressure piston (29) only just before top dead center. Todamp the force of the collision between the two pistons (26) and (29), adamping element (27) is embedded in the top side of the intermediatepiston (26). By way of example, the damping element (27) is made of arubber-elastic material. Hydraulic damping is also conceivable.

The fuel stream that is furnished to the high-pressure pump (20) by thelow-pressure pump (3) is controlled by a flow regulating valve (40). Thedesign of the flow regulating valve is shown in simplified form in FIG.2.

The flow regulating valve (40) here has an approximately parallelepipedhousing (41) with a central slide bore (42). This bore is embodied as ablind bore, in which a longitudinal slide (60) is inserted, slidingtightly. Around the rear region of the blind bore, the housing (41) isembodied approximately cylindrically. The cylindrical outer face extendscoaxially with the slide bore (42). Seated on the outer face is anelectromagnetic drive (74). By way of example, this drive is aproportional magnet.

The slide bore (42), on its open end or in other words on the left inFIG. 2, has a thread (43) by way of which a connection neck (50) issecured to the housing (41). Located on the right next to the outlet ofthe thread (43) is an annular groove (45), into which a return bore (46)discharges radially. Disposed in the middle region of the slide bore(42) is a second annular groove (47), into which a radially orientedbore (48) likewise discharges.

The longitudinal slide (60) has primarily a cylindrical contour. In itsmiddle region, it has a transverse bore (64), which intersects thecenter line of the longitudinal slide and whose cross section is on theorder of magnitude of the individual cross sections of the bores (46)and (48). Extending toward this transverse bore (64) from the left faceend is stepped bore (61), both of whose portions are orientedconcentrically to the outer contour of the longitudinal slide (60). Thefirst portion (62), which begins at the left face end, has a largerdiameter than the second portion. At the transition between theseportions there is a plane shoulder (63), on which a nozzle disk (71)rests. The nozzle disk (71) has a central throttle bore (72). It isretained on the shoulder (63) with the aid of a helical spring (75),which is braced on the connection neck (50) in a recess (52) that isgeometrically comparable to the portion (62).

Located between the transverse bore 64 and the right-hand plane face endof the longitudinal slide (60) is a central relief bore (65) of smalldiameter.

The cylindrical outer contour of the longitudinal slide (60) has a waist(67) or flat annular groove in a region to the right next to thetransverse bore (64). The transverse bore (64) discharges into the waist(67). The left-hand edge of the waist (67) forms a control edge (68),whose spacing from the annular groove (47) is approximately equivalentto the spacing between the left end face of the longitudinal slide (60)and the annular groove (45). The length of the waist (67) is at leastequal to the maximum stroke of the longitudinal slide (60).

In the basic position of the flow regulating valve (40), thelongitudinal slide (60) rests on the bottom of the slide bore (42). Whenthe drive (74) is without electric current, as shown here, the force ofthe helical spring (75) keeps the longitudinal slide (60) in thisposition. The spring force may be varied by placing one or more spacerdisks underneath between the collar (51) of the connection neck (50) andthe left end face of the housing, next to a sealing ring (53). Via theconnection neck (50), which is supplied by the low-pressure pump (3),fuel flows into the interior of the housing (41). This fuel fills theentire slide bore (42) next to the longitudinal slide (60). It flowsnearly unthrottled via the return bore (46) into the return line (13);see FIG. 1. Since the control edge (68) that defines the waist (67) onthe left is positioned on the right outside the annular groove (47), thefeed bore (48) and the low pressure line (12) connected to it--see FIG.1--are not supplied with fuel.

With the delivery of electric current to the electromagnetic drive (74),the longitudinal slide (60) moves to the left. As soon as the controledge (68) passes under the annular groove (47), fuel is supplied to thehigh-pressure pump (20) via the feed bore (48) and the low pressure line(12) adjacent to it. At the same time, a new force equilibrium isestablished at the longitudinal slide (60). When the annular groove (47)is opened, the fuel pressure in the longitudinal slide (60) on the rightnext to the throttle disk (71) drops. The annular groove (45) locatedfarthest to the left is also closed by the extent to which the annulargroove (47) opens. The total force, made up of the force of the helicalspring (75) and the force from the pressure difference on either side ofthe throttle disk (71), now acts upon the left face end of thelongitudinal slide (60). The force of the electromagnetic drive (74)acts in the opposite direction. Since the spring force and the hydraulicforce are regionally nearly constant, the fuel stream flowing into thelow pressure line (12) can be varied by varying the magnetic force orthe electric current. By suitably controlling the electromagnetic drive(74), it is possible to supply the high-pressure pump (20) with aconstant fuel stream, as long as this stream is below the volumetricflow pumped by the low-pressure pump (3). The remaining flow then entersthe return loop via the return bore (46).

If maximum current is supplied to the electromagnetic drive (74), thelongitudinal slide (60) moves so far to the left that its outer contourcompletely covers the annular groove (45). The entire fuel stream istransported into the low pressure line (12), via the stepped bore (61),the transverse bore (64), the waist (67), the annular groove (47), andthe feed bore (48).

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

What is claimed is:
 1. A system for generating high fuel pressure for afuel injection system used in internal combustion engines, whichcomprises, a high pressure pump, a low-pressure pump (3) which aspiratesfuel from a fuel tank (1) and delivers the fuel via a low pressure line(12) and at least one valve to said high-pressure pump (20), some of thefuel stream being diverted to a return loop from the low pressure line(12) upstream of the high-pressure pump (20), a flow regulating valve(40) is disposed in the low pressure line (12), which under anelectrical open loop control delivers the fuel stream, furnished by thelow-pressure pump (3) to the high-pressure pump (20) and under anelectrical closed loop control, said flow regulating valve delivers thefuel stream furnished by the low pressure pump (3) to the return loop,said flow regulating valve (40) is an electromagnetically actuatedlongitudinal slide valve, having an electromagnetic drive (74) whichoperates counter to at least a restoring spring (75), said flowregulating valve includes a longitudinal slide (60), said longitudinalslide (60) is acted upon by low pressure on a face end facing theelectromagnetic drive (74) and, in a region of said face end has athrottle valve (72) by way of which when the flow regulating valve (40)is actuated, fuel flows into a portion of the low pressure line (12)that leads onward to the high-pressure pump (20).